Dimensionally stable closed cell rigid polyisocyanate based foam prepared from a froth foaming mixture

ABSTRACT

There is now provided a closed cell rigid polyisocyanate based foam blown with a C 1  -C 4  hydrofluorocarbon and formic acid as blowing agents, which possesses a uniform density gradient varying by not more than 10 percent. There is also now provided a polyol composition and a froth foaming mixture having good flow by employing a polyol and formic acid in the presence of a C 1  -C 4  hydrofluorocarbon having a boiling point of 300 K or less as co-blowing agents. The polyol composition advantageously has an average OH number of less than 400 and an average functionality of greater than 4, which when reacted with the isocyanate in the presence of a C 1  -C 4  hydrofluorocarbon, yields a rigid closed cell polyisocyanate based dimensionally stable foam having a fine cell structure.

1. FIELD OF THE INVENTION

The present invention pertains to polyol compositions and dimensionallystable closed cell rigid polyisocyanate based foams made thereby, andmore particularly to foaming reaction mixtures which froth at adispensing head and which have excellent flow characteristics, employingas a blowing agents a C₁ -C₄ hydrofluorocarbon having a boiling point of300 K or less, preferably 1,1,1,2-tetrafluroethane, and formic acid orsalts thereof.

2. BACKGROUND OF THE INVENTION

Various hydrofluorocarbons have been investigated in the industry asblowing agents for polyisocyanate based foams due to their low ornonexistent ozone depletion potentials. U.S. Pat. No. 4,997,706discloses the use of closed cell rigid polyurethane foams blown with aC₁ -C₄ hydrofluorocarbon along with a blowing agent precursor such aswater in amounts effective to lower the thermal conductivity of the foamrelative to a similar foam made in the absence of the hydrofluorocarbon.Such rigid thermal insulation foams are generally poured or sprayed intoa cavity or mold to make residential or commercial refrigerationcabinets, entry doors, or other applications where insulation isadvantageous. The cavities into which the foaming mixture is poured orsprayed are often large and/or contain complex shapes which make itdifficult for the foaming mixture to uniformly penetrate. In the case ofa large cavity, the foam front begins to gel making it increasinglydifficult for the mixture to cover the whole cavity and foam to auniform density. The advantageous thermal insulation properties of thefoam are defeated if gaps are left in the cavity where the foamingmixture could not penetrate, if bubbles form as a result of the foamshrinking due to poor dimensional stability, or if the density gradientis non-uniform which in turn leads to gaps or poor dimensionalstability.

The flow characteristics of a foaming mixture becomes particularlycritical when one employs a blowing agent which instantly volatilizes atatmospheric pressure and temperature, causing the foam to froth at thedispensing head. An example of such a blowing agent is1,1,1,2-tetrafluoroethane (R-134a). A frothed foam has the consistencymuch like a shaving cream, which renders it difficult to evenly flowthroughout a cavity.

When manufacturing a rigid closed cell polyisocyanate based foam in acavity or pour in place application, the average hydroxyl number of thepolyols are generally over 400 to increase the crosslinking density,provide structural strength, and prevent foam shrinkage. The higher theaverage hydroxyl number, however, the more isocyanate one must consumeat an equivalent isocyanate index and the faster the ingredients react.It would be desirable to increase the formulation latitude andprocessing window by decreasing the average hydroxyl number of thepolyols, with the attendant advantage of reducing the amount ofisocyanate consume and slowing the reaction down to afford improved flowcharacteristics. Adding high levels of blow catalyst in an effort toimprove flow actually impedes the flow and impairs foam propertiesbecause the high levels of catalyst too rapidly promote the formation ofurethane foam matrix. Merely lowering the average hydroxyl number,however, typically results in sacrificing dimensional stability.

It would also be desirable to reduce the amount of hydrofluorocarbon,such as R-134(a), employed due to its cost, while retaining the samedensity of a foam blown with the original amount of thehydrofluorocarbon. Merely adding more water, however, tends to gel thefoam quicker, which reduces the flow characteristics of the foamingmixture, degrades the dimensional stability of the foam, and causes thefoam to have a coarse cell structure.

3. SUMMARY OF THE INVENTION

There is now provided a closed cell rigid polyisocyanate based foamhaving a closed cell content of at least 85% blown with a combination ofa C₁ -C₄ hydrofluorocarbon having a boiling point of 300 K or less,preferably 1,1,1,2-tetrafluroethane, and formic acid or salts of formicacid. The foam advantageously has a uniform density gradient varying bynot more than 10 percent and a fine cell structure. A foam with a gooddensity gradient indicates that the foaming mixture flowed well.

There is also provided a polyol composition comprising a) compoundshaving at least two isocyanate reactive hydrogens, b) formic acid orsalts of formic acid, and c) a C₁ -C₄ hydrofluorocarbon having a boilingpoint of 300 K or less, preferably 1,1,1,2-tetrafluoroethane. In oneembodiment, the a) compounds are hydroxyl terminated polyols having anaverage OH number of less than 400 and an average functionality ofgreater than 4, which when reacted with the isocyanate in the presenceof a C₁ -C₄ hydrofluorocarbon, yields a mixture which has good flow anda rigid closed cell polyisocyanate based dimensionally stable foam.

Also described is a method of making a closed cell rigid polyisocyanatebased foam having a closed cell content of at least 85%, comprisingejecting through a dispensing head an isocyanate stream and a polyolcomposition stream at a weight ratio of 0.9:1 to 1.3:1, respectively, inthe presence of a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less, wherein the polyol composition stream comprises a) compoundshaving at least two isocyanate reactive hydrogens; and b) formic acid orsalts of formic acid.

The formulations described herein have the advantage of reducing theamount of C₁ -C₄ hydrofluorocarbon needed without sacrificing thedimensional stability of the foam or the flow characteristics of thefoaming mixture at densities equivalent to the higher levels ofhydrofluorocarbon which would otherwise have to be employed.

4. DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following terms of art are to be understoodaccording to the accompanying definitions:

A "uniform density gradient" means that the overall density of the foamdoes not vary by more than 10 percent from the core density taken fromthe same foam. The percentage variation is measured according to thefollowing formula: ##EQU1## where O.D. is the overall density and C.D.is the core density The panel is packed to 10 percent beyond thetheoretical value needed to completely fill the mold volume, and thefree rise density of the foaming mixture employed is 1.9 pcf or less.The test is run by using a foam panel measured and taken from a 2'×4'×2"mold from which the overall density is measured, and a core samplemeasuring 3"×3"×1" taken from any point along the length of the paneland at about the center of its width. Test panels which do not have theabove measurements across the entire respective surfaces are not usedfor determining the density gradient and would in any case indicateextremely poor flow characteristics. At no point should the densitygradient anywhere on the foam panel vary by more than 10 percent.

A "polyol composition" contains at least formic acid as a blowing agentand a compounds having at least two isocyanate reactive hydrogens.

A "compound having at least two isocyanate active hydrogens" has anumber average molecular weight of greater than 400.

A "froth foaming mixture" is a combination of a polyol compositionstream and an organic polyisocyanate stream in the presence of a C₁ -C₄hydrofluorocarbon which may be mixed with the polyol composition, thepolyisocyanate stream, or both; where the C₁ -C₄ hydrofluorocarbonsufficiently and spontaneously vaporizes when the two combined streamsare exposed to atmospheric pressure upon discharge from the dispensinghead to produce a froth. It is to be understood that not all of the C₁-C₄ hydrofluorocarbon needs to vaporize instantaneously from the twostream mixture when discharged, but at least an amount sufficient toproduce a froth upon discharge and prior to entry into a cavity or ontoa substrate.

Turning to the polyol composition, there is provided an a) compoundhaving at least two isocyanate active hydrogens and b) formic acid orsalts of formic acid. In one embodiment, the C₁ -C₄ hydrofluorocarbon isadded to the a) and b) compounds to form a polyol composition. Inanother embodiment, the hydrofluorocarbon can be added only to theisocyanate compound, or it can be added to both the isocyanate and aspart of the polyol composition.

The compounds having at least two isocyanate active hydrogens have anaverage hydroxyl number ranging from 150 to 800 mgKOH/g of compoundhaving at least two isocyanate active hydrogens. In a preferredembodiment, however, the average hydroxyl number is less than 400 andthe average functionality is greater than 4.0., and more preferably, theaverage hydroxyl number is 350 or less and the average functionality is4.5 or more. These average hydroxyl numbers are unusual in that thetypical rigid polyurethane foam is made with polyols whose averagehydroxyl number exceeds 400 so as to provide the rigidity and structuralstrength necessary to make a dimensionally stable foam. However, in thepresent invention, a dimensionally stable foam is provided with a polyolcombination that has a low average hydroxyl number. Further, byproviding a low average hydroxyl number, the flow characteristics of thefroth foaming mixture are enhanced, and less isocyanate is consumed atany given isocyanate index. It is to be understood that in the preferredembodiment, compounds having at least two isocyanate active hydrogenswhose hydroxyl numbers exceed 400 can be employed so long as the averagehydroxyl number of all such compounds is less than 400. The a) compoundsare also preferably hydroxyl terminated compounds such aspolyoxyalkylene polyether polyols, polyester polyols, or mixturesthereof

Examples of compounds having at least two isocyanate active hydrogensinclude polythioether polyols, polyester amides and polyacetalscontaining hydroxyl groups, aliphatic polycarbonates containing hydroxylgroups, amine terminated polyoxyalkylene polyethers, and preferably,polyester polyols, polyoxyalkylene polyether polyols, and graftdispersion polyols. In addition, mixtures of at least two of theaforesaid polyols can be used as long as the combination has an averagehydroxyl number in the aforesaid range.

The term "polyester polyol" as used in this specification and claimsincludes any minor amounts of unreacted polyol remaining after thepreparation of the polyester polyol and/or unesterified polyol (e.g.,glycol) added after the preparation of the polyester polyol. Thepolyester polyol can include up to about 40 weight percent free glycol.

Suitable polyester polyols can be produced, for example, from organicdicarboxylic acids with 2 to 12 carbons, preferably aliphaticdicarboxylic acids with 4 to 6 carbons, and multivalent alcohols,preferably diols, with 2 to 12 carbons, preferably 2 to 6 carbons.Examples of dicarboxylic acids include succinic acid, glutaric acid,adipic acid, suberic acid, azelaic acid, sebacic acid,decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid,isophthalic acid, and terephthalic acid. The dicarboxylic acids can beused individually or in mixtures. Instead of the free dicarboxylicacids, the corresponding dicarboxylic acid derivatives may also be usedsuch as dicarboxylic acid mono- or di- esters of alcohols with 1 to 4carbons, or dicarboxylic acid anhydrides. Dicarboxylic acid mixtures ofsuccinic acid, glutaric acid and adipic acid in quantity ratios of20-35:35-50:20-32 parts by weight are preferred, especially adipic acid.Examples of divalent and multivalent alcohols, especially diols, includeethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropyleneglycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,10-decanediol, glycerine and trimethylolpropanes, tripropylene glycol,tetraethylene glycol, tetrapropylene glycol, tetramethylene glycol,1,4-cyclohexane-dimethanol, ethanediol, diethylene glycol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or mixtures of at leasttwo of these diols are preferred, especially mixtures of 1,4-butanediol,1,5-pentanediol, and 1,6-hexanediol. Furthermore, polyester polyols oflactones, e.g., ε-caprolactone or hydroxycarboxylic acids, e.g.,ω-hydroxycaproic acid, may also be used.

The polyester polyols can be produced by polycondensation of organicpolycarboxylic acids, e.g., aromatic or preferably aliphaticpolycarboxylic acids and/or derivatives thereof and multivalent alcoholsin the absence of catalysts or preferably in the presence ofesterification catalysts, preferably in an atmosphere of inert gases,e.g., nitrogen, carbon dioxide, helium, argon, etc., in the melt attemperatures of 150° to 250° C., preferably 180° to 220° C., optionallyunder reduced pressure, up to the desired acid value which is preferablyless than 10, especially less than 2. In a preferred embodiment, theesterification mixture is subjected to polycondensation at thetemperatures mentioned above up to an acid value of 80 to 30, preferably40 to 30, under normal pressure, and then under a pressure of less than500 mbar, preferably 50 to 150 mbar. The reaction can be carried out asa batch process or continuously. When present, excess glycol can bedistilled from the reaction mixture during and/or after the reaction,such as in the preparation of low free glycol-containing polyesterpolyols usable in the present invention. Examples of suitableesterification catalysts include iron, cadmium, cobalt, lead, zinc,antimony, magnesium, titanium and tin catalysts in the form of metals,metal oxides or metal salts. However, the polycondensation may also bepreformed in liquid phase in the presence of diluents and/orchlorobenzene for aziotropic distillation of the water of condensation.

To produce the polyester polyols, the organic polycarboxylic acidsand/or derivatives thereof and multivalent alcohols are preferablypolycondensed in a mole ratio of 1:1-1.8, more preferably 1:1.05-1.2.

After transesterification or esterification, the reaction product can bereacted with an alkylene oxide to form a polyester polyol mixture. Thisreaction desirably is catalyzed. The temperature of this process shouldbe from about 80° to 170° C., and the pressure should generally rangefrom about 1 to 40 atmospheres.

While the aromatic polyester polyols can be prepared from substantiallypure reactant materials, more complex ingredients are advantageouslyused, such as the side stream, waste or scrap residues from themanufacture of phthalic acid, terephthalic acid, dimethyl terephthalate,polyethylene terephthalate, and the like.

Other residues are DMT process residues, which are waste or scrapresidues from the manufacture of dimethyl terephthalate (DMT). The term"DMT process residue" refers to the purged residue which is obtainedduring the manufacture of DMT in which p-xylene is converted throughoxidation and esterification with methanol to the desired product in areaction mixture along with a complex mixture of byproducts. The desiredDMT and the volatile methyl p-toluate byproduct are removed from thereaction mixture by distillation leaving a residue. The DMT and methylp-toluate are separated, the DMT is recovered and methyl p-toluate isrecycled for oxidation. The residue which remains can be directly purgedfrom the process or a portion of the residue can be recycled foroxidation and the remainder diverted from the process or, if desired,the residue can be processed further as, for example, by distillation,heat treatment and/or methanolysis to recover useful constituents whichmight otherwise be lost, prior to purging the residue from the system.The residue which is finally purged from the process, either with orwithout additional processing, is herein called DMT process residue.

Polyoxyalkylene polyether polyols, which can be obtained by knownmethods, are particularly preferred for use as the compounds having atleast two isocyanate active hydrogens. For example, polyether polyolscan be produced by anionic polymerization with alkali hydroxides such assodium hydroxide or potassium hydroxide or alkali alcoholates, such assodium methylate, sodium ethylate, or potassium ethylate or potassiumisopropylate as catalysts and with the addition of at least oneinitiator molecule containing 2 to 8, preferably 3 to 8, reactivehydrogens or by cationic polymerization with Lewis acids such asantimony pentachloride, boron trifluoride etherate, etc., or bleachingearth as catalysts from one or more alkylene oxides with 2 to 4 carbonsin the alkylene radical. Any suitable alkylene oxide may be used such as1,3-propylene oxide, 1,2- and 2,3-butylene oxide, amylene oxides,styrene oxide, and preferably ethylene oxide and 1,2-propylene oxide andmixtures of these oxides. The polyalkylene polyether polyols may beprepared from other starting materials such as tetrahydrofuran andalkylene oxide-tetrahydrofuran mixtures; epihalohydrins such asepichlorohydrin; as well as aralkylene oxides such as styrene oxide. Thepolyalkylene polyether polyols may have either primary or secondaryhydroxyl groups, preferably secondary hydroxyl groups from the additionof propylene oxide onto an initiator because these groups are slower toreact.

Included among the polyether polyols are polyoxyethylene glycol,polyoxypropylene glycol,polyoxybutylene glycol, polytetramethyleneglycol, block copolymers, for example, combinations of polyoxypropyleneand polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethyleneglycols, poly-1,4-tetramethylene and polyoxyethylene glycols, andcopolymer glycols prepared from blends or sequential addition of two ormore alkylene oxides. The polyalkylene polyether polyols may be preparedby any known process such as, for example, the process disclosed byWurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp.257-262, published by Interscience Publishers, Inc. (1951) or in U.S.Pat. No. 1,922,459.

Polyethers which are preferred include the alkylene oxide additionproducts of polyhydric alcohols such as ethylene glycol, propyleneglycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, hydroquinone,resorcinol glycerol, glycerine, 1,1,1-trimethylol-propane,1,1,1-trimethylolethane, pentaerythritol, 1,2,6-hexanetriol, a-methylglucoside, sucrose, and sorbitol. Also included within the term"polyhydric alcohol" are compounds derived from phenol such as2,2-bis(4-hydroxyphenyl)-propane, commonly known as Bisphenol A.

Particularly preferred in the polyol composition is at least one polyolwhich is initiated with a compound having at least two primary orsecondary amine groups, a polyhydric alcohol having 4 or more hydroxylgroups, such as sucrose, or a mixture of initiators employing apolyhydric alcohol having at least 4 hydroxyl groups and compoundshaving at least two primary or secondary amine groups.

Suitable organic amine initiators which may be condensed with alkyleneoxides include aromatic amines such as aniline,N-alkylphenylene-diamines, 2,4'-, 2,2'-, and 4,4'-methylenedianiline,2,6- or 2,4-toluenediamine, vicinal toluenediamines, o-chloro-aniline,p-aminoaniline, 1,5-diaminonaphthalene, methylene dianiline, the variouscondensation products of aniline and formaldehyde, and the isomericdiaminotoluenes; and aliphatic amines such as mono-, di-, andtrialkanolamines, ethylene diamine, propylene diamine,diethylenetriamine, methylamine, triisopropanolamine,1,3-diaminopropane, 1,3-diaminobutane, and 1,4-diaminobutane. Preferableamines include monoethanolamine, vicinal toluenediamines,ethylenediamines, and propylenediamine.

Suitable polyhydric polythioethers which may be condensed with alkyleneoxides include the condensation product of thiodiglycol or the reactionproduct of a dicarboxylic acid such as is disclosed above for thepreparation of the hydroxyl-containing polyesters with any othersuitable thioether glycol.

The hydroxyl-containing polyester may also be a polyester amide such asis obtained by including some amine or amino alcohol in the reactantsfor the preparation of the polyesters. Thus, polyester amides may beobtained by condensing an amino alcohol such as ethanolamine with thepolycarboxylic acids set forth above or they may be made using the samecomponents that make up the hydroxyl-containing polyester with only aportion of the components being a diamine such as ethylene diamine.

Polyhydroxyl-containing phosphorus compounds which may be used includethose compounds disclosed in U.S. Pat. No. 3,639,542. Preferredpolyhydroxyl-containing phosphorus compounds are prepared from alkyleneoxides and acids of phosphorus having a P₂ O₅, equivalency of from about72 percent to about 95 percent.

Suitable polyacetals which may be condensed with alkylene oxides includethe reaction product of formaldehyde or other suitable aldehyde with adihydric alcohol or an alkylene oxide such as those disclosed above.

Suitable aliphatic thiols which may be condensed with alkylene oxidesinclude alkanethiols containing at least two --SH groups such as1,2-ethanedithiol, 1,2-propanedithiol, 1,2-propanedithiol, and1,6-hexanedithiol; alkene thiols such as 2-butene-1,4-dithiol; andalkyne thiols such as 3-hexyne-1,6-dithiol.

Also suitable as the polyol are polymer modified polyols, in particular,the so-called graft polyols. Graft polyols are well known to the art andare prepared by the in situ polymerization of one or more vinylmonomers, preferably acrylonitrile and styrene, in the presence of apolyether or polyester polyol, particularly polyols containing a minoramount of natural or induced unsaturation. Methods of preparing suchgraft polyols may be found in columns 1-5 and in the Examples of U.S.Pat. No.3,652,639; in columns 1-6 and the Examples of U.S. Pat. No.3,823,201; particularly in columns 2-8 and the Examples of U.S. Pat. No.4,690,956; and in U.S. Pat. No. Pat. 4,524,157; all of which patents areherein incorporated by reference.

Non-graft polymer modified polyols are also useful, for example, thoseprepared by the reaction of a polyisocyanate with an alkanolamine in thepresence of a polyol as taught by U.S. Pat. Nos. 4,293,470; 4,296,213;and 4,374,209; dispersions of polyisocyanurates containing pendant ureagroups as taught by U.S. Pat. No. 4,386,167; and polyisocyanuratedispersions also containing biuret linkages as taught by U.S. Pat. No.4,359,541. Other polymer modified polyols may be prepared by the in situsize reduction of polymers until the particle size is less than 20 μm,preferably less than 10 μm.

The closed cell rigid polyisocyanate based foam of the invention isblown with at least two blowing agents: b) formic acid or salts thereof,and a C₁ -C₄ hydrofluorocarbon having a boiling point of 300 K or less.The blowing agents which can be used may be divided into the chemicallyactive blowing agents which chemically react with the isocyanate or withother formulation ingredients to release a gas for foaming, and thephysically active blowing agents which are gaseous at the exothermfoaming temperatures or less without the necessity for chemicallyreacting with the foam ingredients to provide a blowing gas. Includedwith the meaning of physically active blowing agents are those gaseswhich are thermally unstable and decompose at elevated temperatures.

The b) formic acid, upon contact with an isocyanate group, reacts toinitially liberate carbon monoxide and further decomposes to form anamine with a release of carbon dioxide. Aside from its zero ozonedepletion potential, a further advantage of using formic acid is thattwo moles of gas are released for every mole of formic acid present,whereas a water-isocyanate reaction results in the release of only onemole of gas per mole of water. In both water-isocyanate and formicacid-isocyanate reactions, the isocyanate is consumed and one must add aproportionate excess of isocyanate to compensate for the loss. However,since formic acid is a more efficient blowing agent than water, themoles of formic acid necessary to produce the same moles of gas as awater-isocyanate reaction is greatly reduced, thereby reducing theamount of excess isocyanate and leading to a substantial economicadvantage. The amount of isocyanate needed to make an equivalent densityfoam is 5 to 30 weight percent less when one employs formic acid ormixtures thereof over an all water-blown formulation.

A further advantage of using formic acid in the polyol composition ofthe invention is its contribution of the improved flowability of thereaction mixture. Without being bound to a theory, it is believed thatthe formic acid-isocyanate reaction proceeds in the following two-stepreaction: ##STR1##

It is believed that liberation of carbon monoxide and subsequentlycarbon dioxide in the above reaction proceeds at a slower rate than therelease of carbon dioxide in a water-isocyanate reaction for tworeasons: a) the anhydride is more stable than the carbamic acid formedin a water-isocyanate reaction and, therefore, requires more thermalenergy to decompose, and b) the above reaction is a two step reactionrather than a one step reaction present in a water-isocyanate reaction.Lower exotherms, especially at the onset of the reaction, aresignificant because the energy driving the reaction between theisocyanate and polyols is lowered, thereby enhancing flow and avoiding arapid gel front buildup. In an all water blown system, the reactionbetween the isocyanate and water proceeds quickly and raises theexotherm earlier, thereby promoting a quicker urethane matrix formationas evidenced by the faster gel time. By contrast, the polyurethanematrix formation from the cream to the gel time in the formic acidcontaining polyol composition of the invention does not proceed asquickly due to the lower exotherm at an equivalent point in time. Thelower exotherm and longer gel times are another factor in the inventionwhich allow the reactive mixture to flow further without encounteringthe fast setting urethane matrix in the hotter and higher watercontaining systems.

The b) formic acid/formate ions in the polyol composition may besupplied by addition of formic acid or a mixture of formic acid andsoluble salts of formic acid. Suitable salts of formic acid include theamine or ammonium salts of weakly base mono, di, or trialkylamines,including hydrazine, triethylamine, dimethylbenzylamine, andtriethylenediamine. Many of these tertiary amine salts of formic acidact in a dual capacity as a source of formate ions for gas productionand as a catalyst for the reaction between isocyanate and compoundshaving isocyanate reactive hydrogens. It is preferred that the formateions present in the polyol composition are supplied by the addition ofan excess of formate ion/formic acid equivalents to the number ofcatalytically active tertiary amine equivalents and, more preferred,also to the number of other tertiary amine equivalents including fullysubstituted amine initiated polyoxyalkylene polyether polyols which canreact in situ with formic acid. Suitable examples include an equivalentratio of formate ion/formic acid equivalents to catalytically activetertiary amine sites of at least 1.1:1, and the same would be a suitableexample for the ratio of formate ion/formic acid equivalents to alltertiary amine centers present in the polyol composition.

Suitable concentrations of formic acid are any commercially available,ranging from about 90% pure to 100% pure, with the remainder being waterand in some cases acetic acid depending upon the source.

The polyol composition contains formic acid or a mixture of formic acidand salts of formic acid, and one may add additional chemically reactiveblowing agents such as water, tertiary alcohols, other 2 to 20 carbonatom mono or poly carboxylic acids having molecular weights from 46 to300 and their amine or ammonium salts. Preferably, water is used as theadditional blowing agent in the polyol composition. Further, water isusually present in commercially available formic acid. Water reacts withthe organic isocyanate to liberate CO₂ gas which is the actual blowingagent. However, since water consumes isocyanate groups, an equivalentmolar excess of isocyanate must be used to make up for the consumedisocyanates.

If organic carboxylic acids are additionally used, suitable exampleswould include aliphatic mon- and polycarboxylic acids, e.g. dicarboxylicacids. However, other organic mono- and polycarboxylic acids are alsosuitable. The organic carboxylic acids may, if desired, also containsubstituents which are inert under the reaction conditions of thepolyisocyanate polyaddition or are reactive with isocyanate, and/or maycontain olefinically unsaturated groups. Specific examples of chemicallyinert substituents are halogen atoms, such as fluorine and/or chlorine,and alkyl, e.g. methyl or ethyl. The substituted organic carboxylicacids could contain at least one further group which is reactive towardisocyanates, e.g. a mercapto group, a primary and/or secondary aminogroup, or preferably a primary and/or secondary hydroxyl group.

Suitable carboxylic acids are thus substituted or unsubstitutedmonocarboxylic acids, e.g. formic acid, acetic acid, propionic acid,2-chloropropionic acid, 3-chloropropionic acid, 2,2-dichlorpropionicacid, hexanoic acid, 2-ethyl-hexanoic acid, cyclohexanecarboxylic acid,dodecanoic acid, palmitic acid, stearic acid, oleic acid,3-mercapto-propionic acid, glycoli acid, 3-hydroxypropionic acid, lacticacid, ricinoleic acid, 2-aminopropionic acid, benzoic acid,4-methylbenzoic acid, salicylic acid and anthranilic acid, andunsubstituted or substituted polycarboxylic acids, preferablydicarboxylic acids, e.g. oxalic acid, malonic acid, succinic acid,fumaric acid, maleic acid, glutaric acid, adipic acid, sebacic acid,dodecanedioic acid, tartaric acid, phthalic acid, isophthalic acid andcitric acid.

Combinations of any of the aforementioned chemically active blowingagents may be employed, such as formic acid, or salts of formic acid,and water.

As a physically active blowing agent, at least a C₁ -C₄hydrofluorocarbon blowing agent having a boiling point of 300 K or less,preferably 273 K or less, is employed in the invention.

Suitable C₁ -C₄ hydrofluorocarbons include difluoromethane (HFC-32);1,1,1,2-tetrafluoroethane (HFC-134a); 1,1,2,2-tetrafluoroethane(HFC-134); 1,1-difluoroethane (HFC-152a); 1,2-difluoroethane (HFC-142),trifluoromethane; heptafluoropropane (R-227a); hexafluoropropane(R-136); 1,1, 1-trifluoroethane; 1,1,2-trifluoroethane; fluoroethane(R-161); 1,1,1,2,2-pentafluoropropane; pentafluoropropylene (R-2125a);1,1,1,3- tetrafluoropropane; tetrafluoropropylene (R-2134a);difluoropropylene (R-2152b); 1,1,2,3,3-pentafluoropropane; and1,1,1,3,3-pentafluoro-n-butane.

In a preferred embodiment, the physically active blowing agent is atleast 1,1,1,2-tetrafluoroethane (R-134a), and more preferably R-134a isthe sole physically active blowing agent used because of its wideavailability, its zero ozone depletion potential, and its excellentfrothing characteristics. R-134a has a boiling point of 247 K (-26° C.at 760 mm/Hg) and readily vaporizes at atmospheric pressure to froth afoaming mixture as it exits a dispensing head. R-134a, and other C₁ -C₄hydrofluorocarbons, may be added to the polyol composition at thedispensing head as a separate stream; blended into the polyolcomposition tank immediately prior to dispensing; pre-blended into thepolyol composition, stored and shipped in pressurized containers to afoam manufacturer, added to the isocyanates in the isocyanate stream, oradded to both the polyol composition and the isocyanate stream. To makea formulated polyol composition by any of these methods, R-134a, or anyof the other C₁ -C₄ hydrofluorocarbons, is liquified if necessary underpressure, metered to the polyol composition, and optionally butpreferably blended until a homogenous solution is formed. Tankscontaining the polyol composition are pressurized at 200-300 psig, anddepending on the type of dispensing method employed as discussed furtherbelow, may also be pressurized with an inert gas such as nitrogen.

The amount of C₁ -C₄ hydrofluorocarbons employed, including R-134a, willdepend upon the desired density and the limits of its solubility in aparticular polyol composition. To reduce costs, it is alwaysadvantageous to keep the amount of hydrofluorocarbon to a minimum withinthe desired density range.

In the polyol composition of the invention, amounts of formic acid/saltsare generally used are generally from 2.0 weight percent to 7.0 weightpercent, with 3.5 to 5.5 weight percent being an preferred optimalrange, based on the weight of the polyol composition. Amounts of R-134aadded to the polyol composition range are from 3.0 to 10 parts byweight, preferably from 5 pbw to 9 pbw, based on the weight of the frothfoaming composition which includes the isocyanate and polyolcomposition. With regard to R-134(a), at amounts of less than 3.0 weightpercent, such as about 2 weight percent based on the weight of the frothfoaming composition, the foaming mixture does not froth. Therefore, toform a froth, at least 3.0 weight percent of R-134a should be used,based on the weight of the foaming composition. At these amounts ofR-134a and formic acid, we have been able to produce rigid closed cellpolyisocyanate based foams having low free rise densities ranging from1.5 pcf to 1.9 pcf and low overall molded densities ranging from 2.0 pcfto 2.5 pcf, more preferably from 2.1 pcf to 2.3 pcf.

Other physically active blowing agents which may be used in combinationwith the b) formic acid or salts thereof and the C₁ -C₄hydrofluorocarbon are those which boil at the exotherm foamingtemperature or less, preferably at 50° C. or less. The most preferredphysically active blowing agents are those which have an ozone depletionpotential of 0.05 or less. Examples of physically active blowing agentsare the volatile non-halogenated hydrocarbons having two to seven carbonatoms such as alkanes, alkenes, cycloalkanes having up to 6 carbonatoms, dialkyl ethers, cycloalkylene ethers and ketones;hydrochlorofluorocarbons (HCFCs); hydrofluorocarbons (HFCs) having morethan 4 carbon atoms or which boil at more than 300 K; perfluorinatedhydrocarbons (HFCs); fluorinated ethers (HFCs); and decompositionproducts.

Examples of volatile non-halogenated hydrocarbons include linear orbranched alkanes, e.g. butane, isobutane, 2,3 dimethylbutane, n- andisopentane and technical-grade pentane mixtures, n- and isohexanes, n-and isoheptanes, n- and isooctanes, n- and isononanes, n- andisodecanes, n- and isoundecanes, and n- and isododecanes. Since verygood results are achieved with respect to the stability of emulsions,the processing properties of the reaction mixture and the mechanicalproperties of polyurethane foam products produced when n-pentane,isopentane or n-hexane, or a mixture thereof is used, these alkanes arepreferably employed. Furthermore, specific examples of alkenes are1-pentene, 2-methylbutene, 3-methylbutene, and 1-hexene, of cycloalkanesare cyclobutane, preferably cyclopentane, cyclohexane or mixturesthereof, specific examples of linear or cyclic ethers are dimethylether, diethyl ether, methyl ethyl ether, vinyl methyl ether, vinylethyl ether, divinyl ether, tetrahydrofuran and furan, and specificexamples of ketones are acetone, methyl ethyl ketone and cyclopentanone.Preferentially, cyclopentane, n- and isopentane, n-hexane, and mixturesthereof are employed.

Hydrochlorofluorocarbon blowing agents include1-chloro-1,2-difluoroethane; 1-chloro-2,2- difluoroethane (142a); 1-chloro-1,1-difluoroethane (142b); 1,1-dichloro-1-fluoroethane (141b);1-chloro-1,1,2-trifluoroethane; 1-chloro-1,2,2-trifluoroethane;1,1-dichloro-1,2-difluoroethane; 1-chloro-1,1,2,2-tetrafluoroethane(124a); 1-chloro-1,2,2,2-tetrafluoroethane (124); 1,1-dichloro-1,2,2-trifluoroethane; 1,1-dichloro-2,2,2-trifluoroethane (123); and1,2-dichloro-1,1,2-trifluoroethane (123a); monochlorodifluoromethane(HCFC-22); 1-chloro-2,2,2-trifluoroethane (HCFC-133a);gem-chlorofluoroethylene (R-1131a); chloroheptafluoropropane (HCFC-217);chlorodifluoroethylene (HCFC-1122); and trans-chlorofluoroethylene(HCFC-1131). The most preferred hydrochlorofluorocarbon blowing agent is1,1-dichloro-1-fluoroethane (HCFC-141b).

Perfluorocarbons or fluorinated ethers include hexafluorocyclopropane(C-216); octafluorocyclobutane (C-318); perfluorotetrahydrofuran;perfluoroalkyl tetrahydrofurans; perfluorofuran; perfluoro-propane,-butane, -cyclobutane, -pentane, -cyclopentane, and -hexane,-cyclohexane, -heptane, and -octane; perfluorodiethyl ether;perfluorodipropyl ether; and perfluoroethyl propyl ether.

Catalysts may be employed which greatly accelerate the reaction of thecompounds containing hydroxyl groups and with the modified or unmodifiedpolyisocyanates. Examples of suitable compounds are cure catalysts whichalso function to shorten tack time, promote green strength, and preventfoam shrinkage. Suitable cure catalysts are organometallic catalysts,preferably organotin catalysts, although it is possible to employ metalssuch as lead, titanium, copper, mercury, cobalt, nickel, iron, vanadium,antimony, and manganese. Suitable organometallic catalysts, exemplifiedhere by tin as the metal, are represented by the formula: R_(n) Sn X--R¹--Y!₂, wherein R is a C₁ -C₈ alkyl or aryl group, R¹ is a C₀ -C₁₈methylene group optionally substituted or branched with a C₁ -C₄ alkylgroup, Y is hydrogen or an hydroxyl group, preferably hydrogen, X ismethylene, an --S--, an --SR² COO--, --SOOC--, an --O₃ S--, or an--OOC--group wherein R² is a C₁ -C₄ alkyl, n is 0 or 2, provided that R¹is C₀ only when X is a methylene group. Specific examples are tin (II)acetate, tin (II) octanoate, tin (II) ethylhexanoate and tin (II)laurate; and dialkyl (1-8C) tin (IV) salts of organic carboxylic acidshaving 1-32 carbon atoms, preferably 1-20 carbon atoms, e.g., diethyltindiacetate, dibutyltin diacetate, dibutyltin diacetate, dibutyltindilaurate, dibutyltin maleate, dihexyltin diacetate, and dioctyltindiacetate. Other suitable organotin catalysts are organotin alkoxidesand mono or polyalkyl (1-8C) tin (IV) salts of inorganic compounds suchas butyltin trichloride, dimethyl- and diethyl- and dibutyl- anddioctyl- and diphenyl- tin oxide, dibutyltin dibutoxide,di(2-ethylhexyl) tin oxide, dibutyltin dichloride, and dioctyltindioxide. Preferred, however, are tin catalysts with tin-sulfur bondswhich are resistant to hydrolysis, such as dialkyl (1-20C) tindimercaptides, including dimethyl-, dibutyl-, and dioctyl- tindimercaptides.

Tertiary amines also promote urethane linkage formation, and includetriethylamine, 3-methoxypropyldimethylamine, triethylenediamine,tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl- andN-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine,N,N,N',N'-tetramethylbutanediamine or -hexanediamine, N,N,N'-trimethylisopropyl propylenediamine, pentamethyldiethylenetriamine,tetramethyldiaminoethyl ether, 2-dimethyaminoethyl-1,3-dimethylaminopropyl ether, N,N-dimorpholinoethylether, bis(dimethylaminopropyl)urea, dimethylpiperazine,1-methyl-4-dimethylaminoethylpiperazine, 1,2-dimethylimidazole,1-azabicylo 3.3.0!octane and preferably 1,4-diazabicylo 2.2.2!octane,and alkanolamine compounds, such as triethanolamine,triisopropanolamine, N-methyl- and N-ethyldiethanolamine anddimethylethanolamine.

To prepare polyisocyanurate (PIR) and PUR-PIR foams by the processaccording to the invention, a polyisocyanurate catalyst is employed.Suitable polyisocyanurate catalysts are alkali salts, for example,sodium salts, preferably potassium salts and ammonium salts, of organiccarboxylic acids, expediently having from 1 to 8 carbon atoms,preferably 1 or 2 carbon atoms, for example, the salts of formic acid,acetic acid, propionic acid, or octanoic acid,andtris(dialkylaminoethyl)-,tris(dimethylaminopropyl)-,tris(dimethylaminobutyl)-andthe corresponding tris(diethylaminoalkyl)-s-hexahydrotriazines. However,(trimethyl-2-hydroxypropyl) ammonium formate,(trimethyl-2-hydroxypropyl)ammonium octanoate, potassium acetate,potassium formate and tris(dimethylaminopropyl)-s-hexahydrotriazine arepolyisocyanurate catalysts which are generally used. The suitablepolyisocyanurate catalyst is usually used in an amount of from 1 to 10parts by weight, preferably form 1.5 to 8 parts by weight, based on 100parts by weight of the polyol composition.

The polyol composition may also contain a flame retardant. Examples ofsuitable phosphate flameproofing agents are tricresyl phosphate,tris(2-chloroethyl) phosphate, tris(2-chloropropyl) phosphate, andtris(2,3-dibromopropyl) phosphate. In addition to thesehalogen-substituted phosphates, it is also possible to use inorganic ororganic flameproofing agents, such as red phosphorus, aluminum oxidehydrate, antimony trioxide, arsenic oxide, ammonium polyphosphate(Exolit®) and calcium sulfate, molybdenum trioxide, ammonium molybdate,ammonium phosphate, pentabromodiphenyloxide, 2,3-dibromopropanol,hexabromocyclododecane, dibromoethyldibromocyclohexane, expandablegraphite or cyanuric acid derivatives, e.g., melamine, or mixtures oftwo or more flameproofing agents, e.g., ammonium polyphosphates andmelamine, and, if desired, corn starch, or ammonium polyphosphate,melamine, and expandable graphite and/or, if desired, aromaticpolyesters, in order to flameproof the polyisocyanate polyadditionproducts. In general, from 2 to 40 pbw of said flameproofing agents maybe used based on the weight of the polyol composition and isocyanatestream.

The organic polyisocyanates include all essentially known aliphatic,cycloaliphatic, araliphatic and preferably aromatic multivalentisocyanates. Specific examples include: alkylene diisocyanates with 4 to12 carbons in the alkylene radical such as 1,12-dodecane diisocyanate,2-ethyl-1,4-tetramethylene diisocyanate, 2-methyl-1,5-pentamethylenediisocyanate, 1,4-tetramethylene diisocyanate and preferably1,6-hexamethylene diisocyanate; cycloaliphatic diisocyanates such as1,3- and 1,4-cyclohexane diisocyanate as well as any mixtures of theseisomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane(isophorone diisocyanate), 2,4- and 2,6-hexahydrotoluene diisocyanate aswell as the corresponding isomeric mixtures, 4,4'- 2,2'-, and2,4'-dicyclohexylmethane diisocyanate as well as the correspondingisomeric mixtures and preferably aromatic diisocyanates andpolyisocyanates such as 2,4- and 2,6-toluene diisocyanate and thecorresponding isomeric mixtures 4,4'-, 2,4'-, and 2,2'-diphenylmethanediisocyanate and the corresponding isomeric mixtures, mixtures of 4,4'-and 2,4'-diphenylmethane diisocyanates and polyphenylenepolymethylenepolyisocyanates (polymeric MDI), as well as mixtures of polymeric MDIand toluene diisocyanates. Crude polyisocyanates may also be used in thecompositions of the present invention, such as crude toluenediisocyanate obtained by the phosgenation of a mixture oftoluenediamines or crude diphenylmethane isocyanate obtained by thephosgenation of crude diphenylmethane diamine. The preferred or crudeisocyanates are disclosed in U.S. Pat. No. 3,215,652. The organic di-and polyisocyanates can be used individually or in the form of mixtures.The preferred isocyanate is polymeric MDI.

Frequently, so-called modified multivalent isocyanates, i.e., productsobtained by the partial chemical reaction of organic diisocyanatesand/or polyisocyanates are used. Examples include diisocyanates and/orpolyisocyanates containing ester groups, urea groups, biuret groups,allophanate groups, carbodiimide groups, isocyanurate groups, and/orurethane groups. Specific examples include organic, preferably aromatic,polyisocyanates containing urethane groups and having an NCO content of33.6 to 15 weight percent, preferably 31 to 21 weight percent, based onthe total weight, e.g., with low molecular weight diols, triols,dialkylene glycols, trialkylene glycols, or polyoxyalkylene glycols witha molecular weight of up to 1500; modified 4,4'-diphenylmethanediisocyanate or 2,4- and 2,6-toluene diisocyanate, where examples of di-and polyoxyalkylene glycols that may be used individually or as mixturesinclude diethylene glycol, dipropylene glycol, polyoxyethylene glycol,polyoxypropylene glycol, polyoxyethylene glycol, polyoxypropyleneglycol, and polyoxypropylene polyoxyethylene glycols or -triols.Prepolymers containing NCO groups with an NCO content of 25 to 9 weightpercent, preferably 21 to 14 weight percent, based on the total weightand produced from the polyester polyols and/or preferably polyetherpolyols described below; 4,4'-diphenylmethane diisocyanate, mixtures of2,4'- and 4,4'-diphenylmethane diisocyanate, 2,4,- and/or 2,6-toluenediisocyanates or polymeric MDI are also suitable. Furthermore, liquidpolyisocyanates containing carbodiimide groups having an NCO content of33.6 to 15 weight percent, preferably 31 to 21 weight percent, based onthe total weight, have also proven suitable, e.g., based on 4,4'- and2,4'- and/or 2,2'-diphenylmethane diisocyanate and/or 2,4'- and/or2,6-toluene diisocyanate. The modified polyisocyanates may optionally bemixed together or mixed with unmodified organic polyisocyanates such as2,4'- and 4,4'-diphenylmethane diisocyanate, polymeric MDI, 2,4'-and/or2,6-toluene diisocyanate.

While the isocyanate compound stream may be mixed with the polyolcomposition stream at a wide range of weight ratios, an advantageousfeature of the formulated polyol composition allows one to mix the twostreams at a weight ratio of from 0.9:1 to 1.3:1 respectively,preferably at a 1.05 to 1.15:1 weight ratio, and at an isocyanate indexranging from 100 to 130, preferably at 105 to 120, while obtaining afoam having excellent dimensional stability at the low densitiesmentioned above. Prior polyurethane foam formulations, however, werereacted at an iso/polyol weight ratio of from about 1.5:1 to 2:1 atisocyanate indices of 100 to 130, which required a larger amount ofisocyanate to stoichiometrically react with the isocyanate reactivegroups at equivalent isocyanate indices. Thus, the formulation of theinvention and the method of dispensing allows one to manufacture adimensionally stable foam using much smaller quantities of isocyanate.

In another feature of the invention, the froth foaming mixture can bedispensed at a constant flow regardless of pressure changes at theoutlet of the dispensing head, thus obviating the need for usingpositive displacement flow control units or for metering the iso streamand polyol stream into the dispensing head at different flow rates. Inthis embodiment, the froth foaming mixture can be dispensed from aportable foaming apparatus as disclosed in U.S. Pat. Nos. 3,541,023 and3,769,232, each of which is incorporated herein by reference. While theuse of a static mixing device as the dispensing head is particularlypreferred, the polyol composition along with the C₁ -C₄hydrofluorocarbon frothing agent can be employed in low pressureequipment having rotary mechanical mix dispensing heads or on highpressure equipment using impingement mix dispensing heads.

Typically, the portable foaming apparatus is comprised of at least tworeactants supply tanks, a static mixer having inlets in communicationwith the supply tanks and an outlet for expelling the mixed reactants,means for imposing gas pressure to drive the reactants from the supplytanks, through and out of the static mixer, and flow control units fordelivering the desired ratio of reactants, from their respective tanks,to the static mixer.

One of the supply tanks contains the organic isocyanate reactant or anorganic isocyanate-terminated quasi-prepolymer or prepolymer. Ifdesired, this tank may also contain an additive amount of a non-reactivefire-retardant material which may be used to impart flame retardantproperties to the resulting foam. This tank may also contain R-134a andother non-reactive blowing agents in liquid form, but it is preferred toadd at least part of the R-134a and other blowing agents to the polyolcomposition supply tanks. The other polyurethane foam forming reactantsmay be supplied from one or more additional polyol composition supplytanks. Usually a single second tank is used to supply all these otherreactants, i.e., polyol, foaming agent, catalyst, and surfactant, ifsuch is used.

Any means for imposing pressure to drive the reactants from the supplytanks through and out of the static mixer may be used. Typically, apressurized gaseous inert propellant, such as a nitrogen tank, is usedhaving valved outlets communicating via suitable conduits with theinlets to the supply tanks. The supply tanks are kept under pressure toprovide the driving force needed to propel the reactants from the supplytanks and to liquify the R-134a blowing agent in the formulated polyolcompositions supply tank(s). The pressure in the supply tanks isgenerally 200-250 psig.

It is generally necessary, for the proper functioning of the portablefoaming apparatus, that the viscosity of the contents of each of thesupply tanks be no greater than about 1000 cps at 78° F. and morepreferably no more than about 800 cps. This, of course, means that thematerials in each tanks may have to be properly selected or formulated,as the case may be, in order to meet this viscosity requirement. Theformulated polyol composition according to the invention advantageouslyhas a very low viscosity of 550 cps or less, even lower than 400 cps,rendering the formulation eminently suitable for use in the portablefoaming apparatus. The viscosity values mentioned herein are measured at78° F. and at 80 psig. The viscosity of supply tanks contents aremeasured under a pressure of 80 psig because of the presence of R-134aor other volatile hydrofluorocarbons in liquid form.

The portable foaming apparatus comprises a static mixer which is onecontaining no moving parts. Any such mixer which serves to adequatelyblend the reactants may be used. Illustrative of such a mixer is the onedisclosed in U.S. Pat. No. 3,286,992.

By employing a portable foaming apparatus, the volume ratio of theisocyanate stream to the formulated polyol composition stream can beheld at 1:1±0.1, or as pointed out above, at weight ratio in apreferable range of 1:05 to 1.15:1, thereby reducing the amount ofisocyanate required to make a foam at a desired isocyanate index.

The isocyanate stream and the polyol composition stream are propelled bythe inert gas under pressure into a dispensing head to form a foamablemixture which is ejected from the dispensing head through a static mixerdispensing head as a froth foaming mixture, which is a partiallyexpanded foaming mixture much akin to the consistency of shaving cream,but which continues to expand on or in the application site to its fullmolded or free rise volume. The foamable mixture contains the liquid C₁-C₄ hydrofluorocarbon frothing agent having a boiling point of 300 K orless, and preferably a formulated polyol composition is employed so thatonly two liquid streams enter the dispensing head. Although the foamablemixture exiting the dispensing head, preferably through a static mixer,is in the form of a froth, the froth foaming mixture according to theinvention has excellent flow characteristics as demonstrated by theuniform density gradient of the resulting polyisocyanate based rigidclosed cell foam.

In a more preferred embodiment, the foams made with the formulatedpolyol composition have a uniform density gradient which varies by notmore than 10 percent, most preferably by not more than 6 percent. Thehigh amount of blow catalyst, the low levels of water as a co-blowingagent, the low viscosity of the formulated polyol composition, and thelow average hydroxyl number of the polyols all have a combined effect ofproducing a froth foaming mixture which flows well and produces a lowdensity foam having excellent dimensional stability.

The polyurethane foams made according to the invention are dimensionallystable, meaning that the percent volume change of a 3"×3"×1 core sampletested according to ASTM D 2126-87 taken from a 10 percent overpackedmold measuring 2'×4'×2" is less than ±5 percent, at -20° F., 158° F.,200° F., 100° F. and 100 percent relative humidity, and 158° F. and 100percent relative humidity. Preferably, the percent volume change is lessthan ±4 percent, and more preferably ±3 percent or less.

The polyisocyanate based foams of the invention have a closed cellcontent of at least 85 percent, preferably 90 percent or more, and mostpreferably 95 percent or greater. The foams of the invention also arerigid, meaning that they have a high ratio of compressive strength totensile strength of 0.5:1 or greater and an elongation of 10 percent orless.

Polyurethane foams prepared by the process of the invention have utilityin a variety of applications in which the foam is generated on-site froma portable foaming apparatus. This includes the production of foam-corestructural and architectural panels and partitions, building andvehicular insulation, marine flotation devices, water heater insulation,refrigeration cabinets and panels, entry doors, picnic coolers, and avariety of molded objects for use in home furnishing.

The following examples are intended to illustrate, but in no way limit,the scope of the present invention. The following examples are providedto illustrate the invention. The foaming apparatus used in theseexamples was identical to the apparatus disclosed in U.S. Pat. No.3,769,232 except that it did not include the valved timing assemblyembodied in the apparatus of that patent. Thus, the apparatus comprised(a) a first supply tank for supplying the isocyanate reactant, (b) asecond supply tank for supplying the other foam forming ingredients, (c)a nitrogen pressure tank having a valved outlet in communication, via adistributing valve, with the inlets to the two supply tanks, (d) astatic mixer having one outlet and two inlets communicating with thesupply tanks outlets, and (e) adjustable flow control units interposedin the conduits linking the supply tank with the static mixer.

The polyols employed in the working examples are defined as follows:

    ______________________________________                                        Polyol A   is a propylene oxide/ethylene oxide adduct of                                 a mixture of a vicianl toluene diamine/ethylene                               diamine amine intiators having a nominal                                      OH# of 300, commercially available from                                       BASF Corporation.                                                  Polyol B   is a propylene oxide adduct of a sucrose/amine                                mixture having a nominal hydroxyl number of 530,                              commercially available from Olin Corporation.                      Polyol C   is a propylene oxide adduct of a sucrose/amine                                mixture having a nominal hydroxyl number of 350,                              commercially available from Olin Corporation.                      Niax LS440 is a silicone surfactant commercially available                               from Union Carbide.                                                PCF        is Fyrol PCF, a flame retardant, available from                               Great Lakes Chemical.                                              DABCO 8154 is a 2-ethyl-hexanoic acid blocked triethylene                                diamine, commercially available from Air Products.                 DABCO DC-2 is a delayed action amine based catalyst available                            from Air Products.                                                 ______________________________________                                    

EXAMPLE 1

The portable foaming apparatus referred to above was employed to preparea frothed, rigid, molded polyurethane foam using the procedure andingredients described herein.

The foam forming ingredients were supplied from two cylindrical metaltanks. One supply tank contained the Iso A reactant, namely,polymethylene polyphenylene isocyanate. This material is commerciallyavailable under the trademark LUPRANATE® M20S, a product of BASFCorporation. The other supply tank, the total content of which had aviscosity of 410 cps at 77° F. for sample 2, when measured at 80 psig;contained the following ingredients in Table 1 in the indicated relativeproportions as weight percent.

                  TABLE 1                                                         ______________________________________                                        INGREDIENTS        SAMPLE 1  SAMPLE 2                                         ______________________________________                                        Polyol A           44.92     75.94                                            Polyol B           16.48     17.61                                            Polyol C           25.00     0.0                                              PCF                7.00      0.0                                              L5540              2.0       2.2                                              DABCO DC-2         0.1       0.0                                              DABCO 8154         0.0       0.25                                             FORMIC ACID.sup.1  4.5       4.0                                              TOTAL              100       100                                              R-134a                                                                        PERCENT IN POLYOL COMP.                                                                          7.0       7.0                                              ISO A              100       100                                              R-134a                                                                        PERCENT IN ISO A   7.00      7.00                                             INDEX              110       110                                              WEIGHT RATIO       100/93    100/93                                           OF ISO/POLYOL COMP.                                                           ______________________________________                                         .sup.1 A solution of 94% formic acid in 6% water.                        

Both of the two supply tanks were placed horizontally on a drum rollerand rotated continuously for two hours at an approximate rate of 35revolutions per minute. After the rotation was stopped, the inlets tothe two supply tanks were connected to the nitrogen pressure tank andthe pressure was increased to 240 psig. The tanks outlets were connectedto the static mixer via separate conduits provided with flow controlunits. With the flow control units adjusted to deliver to the staticmixer equal weight proportions from the first and second supply tanks,the foam forming ingredients were expelled, by means of the nitrogenhead pressure, from their respective tanks, through the static mixer,and out into an aluminum mold preheated to 90° F. and having thedimensions 2'×4'×2". The results are reported below in Table 2.

                  TABLE 2                                                         ______________________________________                                        PROPERTIES         SAMPLE 1   SAMPLE 2                                        ______________________________________                                        Density, f.r., 6" Core                                                                            1.4 pcf    1.4 pcf                                        from 2' × 2' × 2' Box                                             Density, f.r., #10 Lily cup                                                                       1.5 pcf    1.5 pcf                                        Gel Time            2'15"      1'50"                                          Tack Free Time      3'30"      3'00"                                          Weight Ratio                                                                  Iso/Resin          100/93     10/93                                           Test Panel 2' × 4' × 2"                                           Overall Density     2.2 pcf    2.25 pcf                                       Core Density        2.05 pcf   2.10 pcf                                       % Vanance           7 percent  7 percent                                      Compressive Strength (yield)                                                  Parallel           26         28                                              Perpendicular      22         21                                              U.L 94 HF-1                                                                   Average Self-Extinguish                                                                          40 seconds 36 seconds                                      Average Damage Length                                                                            46 mm      45 mm                                           % Closed cell, uncorrected                                                                       90         92                                              % Volume Change, 14 Days                                                      -20° F.     -0.1       0.4                                             158° F.     -1.1       -1.5                                            200° F.     -1.0       -1.2                                            100° F. + 100% R.H.                                                                       -2.2       -1.5                                            158° F. + 100% R.H.                                                                       -3.4        2.5                                            ______________________________________                                    

What I claim is:
 1. A polyol composition comprising:a) compounds havingat least two isocyanate reactive hydrogens; b) at least about 2.0 weightpercent formic acid or salto of formic acid based on the total weight ofthe polyol; and c) a C₁ -C₄ hydrofluorocarbon having a boiling point of300K or less, wherein said polyol composition is a solution.
 2. Thepolyol composition of claim 1, wherein said c) compound comprises1,1,1,2-tetrafluoroethane.
 3. The polyol composition of claim 2, wherein80 wt. % or more of said a) compounds comprise polyoxyalkylene polyetherpolyols.
 4. The polyol composition of claim 3, wherein saidpolyoxyalkylene polyether polyols are initiated with initiatorscomprising compounds containing at least two primary or secondary aminegroups.
 5. The polyol composition of claim 4, wherein said initiatorscomprise toluene diamine, a C₂ -C₆ aliphatic polyamine, or mixturesthereof.
 6. The polyol composition of claim 1, wherein the averagehydroxyl number of the polyol composition is less than 400 and theaverage functionality is 4.0 or greater.
 7. The polyol composition ofclaim 2, wherein compound b) comprises formic acid in an amount rangingfrom 2.0-7.0 wt.% or more based on the weight of the polyol composition.8. The polyol composition of claim 2, wherein the amount of1,1,1,2-tetrafluoroethane is 4 p.b.w. or more based on 100 p.b.w. of thecombined weight of said polyol composition and an isocyanate compositioncomprising a compound having at least two isocyanate groups.
 9. Thepolyol composition of claim 2, wherein said b) compound comprises formicacid.